Today there are a number of different commercial tooth systems for replaceable wear and/or replacement parts for tools to an earth moving machine for loosening and breaking more or less hardened earth and rock mass out of a work surface, after which the masses are appropriately removed. An example of such tools and exchangeable wear and/or replacement part is, here, especially comprised by a dredging tool's rotating bore bit, also called a cutter head, with its replaceable wear teeth. Clearly, these tooth systems can also be used for other types of earth moving machinery, such as the bucket to a digger, etc.
Regarding especially cutter heads, said wear teeth, see FIG. 2, are arranged at a given distance from each other, generally helical, elongated along blades protruding from a central body attached to a central, rotating hub. The blades suitably extend in a helical line from the hub at the forward end of the body and rearward in the tool's feed direction to the rear end of the rotating body comprising a back ring, holding the blades together, where also a suction device is arranged for removal of the loosened earthen mass through the interspace between the blades.
Such tooth systems usually comprise two main connection parts in the form of a “female” and a “male” part that together form a full, assembled “tooth” in a series of adjacently arranged teeth along, for example, the bore bit's blades or the bucket's cutting edge. Such a “tooth”, thus, comprises a forward wear-part in the form of a replaceable tooth portion with a (cutting) point and comprising a rear leg for mounting in a specially-designed groove at a rear, stationary holder, which suitably is firmly fixed to, for example, the bore bit. To achieve a dynamic yet reliable attachment of the replaceable tooth point to the holder, the connection parts also comprise a connection system common to the parts and with a detachable locking mechanism. Every such connection system has a distinctively characteristic geometry, comprising the surfaces and the form of the legs and grooves named above, in order to thereby attempt to have the wear-part of each “tooth” held effectively and safely in place in a function-sufficient manner that embodies minimal wear to the wear-part until, due to inevitable wear, the wear-part must be replaced.
Such commercial tooth systems are designed to absorb loads (F) from the use of the tool through specially designed and mutually interactive contact zones, which are arranged along the joint between the connection parts defined by the leg and groove. Each contact zone comprises at least two mutually opposing and interacting contact surfaces arranged one on each connection part and arranged at a given angle to the line of axial symmetry Y of said joint. When these contact surfaces are placed mainly perpendicular to said axial line of symmetry Y, i.e. essentially in the cross vertical plane (XZ), the further insertion of the tooth part on the holder part is stopped completely, why these surfaces are also hereafter referred to as stop surfaces. Another way is to arrange the contact surfaces in a more acute angle to the connection parts' joining direction along the joint, where the load is absorbed by the friction forces generated by the wedging effect of the friction surfaces.
However, it is to be understood that when the tool is used there are not only active loads that are parallel to the connection geometry along with a longitudinal plane of symmetry Y, but also loads that deviate from the Y direction. Essentially, every active load (F), thus, comprises, see FIG. 18, in part a shearing force component, Fc that acts essentially from the front parallel to the work surface and axially placed in relation to the said joint, in part a normal force component Fs that acts essentially from above, perpendicular to the work surface and in part a transverse force component Fp that acts from the side, essentially parallel to the work surface and more perpendicular in relation to said tooth part's protrusion beyond the connection parts' common joint.
The position terms used below such as rear, forward, lower, upper, vertical, transverse or horizontal surfaces, etc., can consequently be inferred from the definitions, as stated above, of said forces and the mutual relationship of the connection parts, as well as their relations and positions relative to the work surface.
The new concept for a tooth system, as stated in the present patent application, comprises a number of characteristics, which characteristics alone or in combination are unique in comparison with the presently available tooth systems and which characteristics afford advantageous solutions to a number of problems that can arise with known tooth systems.
A number of these problems are summarized below.
Among conventional tooth systems it is a fact that despite the tooth system being relatively strong, the contact area along the tooth system's joint, between the tooth holder and tooth point, is too limited. This especially applies at the front end and at the front side (A) of the joint where the loads arising from the tool currently being used are the greatest. This causes far too great surface loads and, thus, also causes a large degree of undesirable wear, which essentially reduces the effective wear life cycle of the tooth system holder. This constitutes the real “bottle neck” of the tooth systems, because the holder is designed to be reused as long as possible and, hence, usually is fixed to the tool in a stationary way, e.g. by a weld, while the tooth is, itself, designed to be worn, and which tooth therefore is fitted in a removable manner to afford replacement as easily and rapidly as possible. The “front side of the joint”, here, actually means the interactive stop surfaces, essentially in the cross vertical plane (XZ), at an impact zone between the holder and the tooth at the beginning of the joint between them, that is, the holder's side that essentially faces the surface worked upon by the tool. Replacement of the holder is, thus, expensive not only due to the intensive time lost but also due to the material parts that have to be discarded.
A consequent problem is that the conventional tooth systems that have all too wide a degree of play between the tooth and holder develop problems with “hammering”, that is, said parts are powerfully impacted against one another during the use of the tool. This hammering causes considerable increase in wear. Those tooth systems that instead have all too narrow a degree of play, that is have a too small gap between the tooth and holder, develop the problem of the tooth becoming difficult to remove from the holder.
Tooth systems designed for earth moving encounter their greatest, and thus, as regards the tooth system design, most often the gravest loads when breaking hard rock. This is due to the very large normal loads Fs that impact essentially perpendicularly to the rock, as such occurs in the course of breaking rock. The known tooth systems, by prior art, thus usually obtain disadvantageous wear damage along the joint between component connection parts of the tooth system, as these lack the required capacity to withstand such Fs loads.
Difficulty in cleaning away dirt and removed earth residues that invariably accumulate in the passages along the holder and tooth, that is, between the joint's contact and clearance surface(s) and also that the holder is difficult to repair on the side essentially facing away from the working surface, that is, the back side are commonly occurring problems with known “leg-type” tooth systems, that is, those tooth systems that have a tooth with a leg that is inserted into a groove in the holder to achieve a joint between the tooth and the holder.
After a period of use the impacting surface forces along the known tooth system's joints shall cause considerable wear and a degree of plastic deformation of the effective parts, which requires expensive and often complicated maintenance. Existing leg-type tooth systems also can not be given increased strength when changing the connection geometry of the joint.
Conventional tooth systems comprise a locking system that is difficult to improve upon in the confined space available between the tooth and holder at the location of the locking device being used and these tooth system do not allow separate types of locking systems and/or modifications to the locking system itself without the tooth's and/or holder's joint first being adapted to the given locking system and/or its modifications.
Further, conventional locking systems, that is, those comprising some form of rigid locking device, e.g. a steel pin, and a locking aperture designed for the locking device, must remove the locking device with a heavier hammer or sledge, which requires considerable work and can cause damage to the locking system and/or the teeth. Thus, it is desirable for the given locking device to be removable and attachable in a simpler and more effective way without incurring any essential risks for such as the said damages arising.
As the locking system wear increases conventional locking systems lose their ability to maintain a retentative force that holds the connection parts together, that is, their pretensioning capacity, which causes the said hammering to worsen significantly and the tooth to finally be destroyed and/or fall out of the tool.
Known tooth systems normally have holder contact surfaces, along the sides of the joint, with high degree of strength, regarding the winch forces (Fs), acting essentially axially along the tooth point that is, the normal forces impacting more or less vertically against the working surface; see FIG. 17, and that are usually absorbed by stop surfaces arranged somewhere along the impact zone between the holder and the tooth, but that are also transferred as friction forces axially along the tooth's axial symmetry axis Y to the contact surfaces along the essentially longitudinal sides along the tooth system's joint. However, the same does not apply to corresponding transverse forces Fp that essentially impact parallel with the breaking surface and, thus, more perpendicular to the tooth's axial symmetry axis Y. These transverse forces (Fp) and those moment forces resulting from them are also essentially absorbed by the contact surfaces along the holder's joint, but said contact surfaces usually have significantly lower strength against such transverse (Fp) and resultant forces.